Conventionally, there has been known a metal bellows for an accumulator into which a hydraulic fluid is drawn in, and which has a bellows-shape in which ridge fold portions on its radially outer side and valley fold portions on its radially inner side are formed repeatedly with slope portions in between. This metal bellows is disposed in a shell of the accumulator, and one end of the metal bellows is fixed to the shell side, whereas another end is closed by a bellows cap. An interior of the shell of the accumulator is partitioned by the bellows cap into a fluid chamber inside the bellows into which the hydraulic fluid is drawn in, and a gas chamber outside the bellows into which a pressure gas is charged. The metal bellows contracts as it discharges the hydraulic fluid from the fluid chamber, and expands as the hydraulic fluid is drawn into the fluid chamber.
As shown in FIG. 3 of Patent Literature 1 and FIG. 2B of Patent Literature 2, when the metal bellows is contracted from a free length, widths of ridge fold portions make almost no change, whereas distances between the adjacent slope portions become smaller in order for the bellows to contract.
When the bellows is in a contracted state, the adjacent slope portions make contact with each other while the widths of the ridge fold portions make no change, and hence the shape of the ridge fold portion becomes a bulb-shape to form a sealed space. If a temperature changes under a condition in which the hydraulic fluid or the pressure gas has entered into the sealed spaces having the bulb-shape, the hydraulic fluid or gas is caused to expand or contract, and hence a stress acting on the metal bellows may increase. If the stress increases excessively, there is a fear that the bellows may break. In addition, if adjacent slope portions make contact with each other, there may be a case where stresses acting on the contacting portions increase, and hence there is a fear that the bellows may break.